Master Cylinder Question - PeachParts Mercedes-Benz Forum

nyko46 · #1 04-01-2010, 04:22 PM

I just change my MB 1984 300 SD master cylinder but I did not bleed it on bench. Instead I try to bleed in the car after installed.
With brake lines disconnected I had someone inside of the car pressing the brake pedal while I was with two of those three line output from master cylinder plugged and trying to get one completely bleed
I used my tomb to plug while brake pedal was traveling up and unplug while traveling down. There was suction when pedal was traveling up but not pressure when traveling down. I tried it many times, I wait for the fluid get inside of the cylinder but everything was unsuccessful.
What can be wrong or what should I do?
The master cylinder was bought as rebuilt unit a long ago and only now I got it installed. I am also trying to find a seal kit to repair the old master cylinder removed but it seems to be a online hard to find part. If you know some place to find please let me know.

Thanks for your help.
Nyck

JohnM. · #2 04-01-2010, 06:14 PM

Sounds like your bleeding procedure is wrong, IMO at least. If I am understanding what you wrote correctly. You should not be plugging anything or disconnecting any brake lines. You are only supposed to open one bleeder valve at a time (on the caliper), starting with the wheel farthest away from the master cylinder and work your way to the closest (RR,LR,RF,LF).....the rest of the system needs to be completely closed. And don't let the reservoir run dry or you'll have to start over.

nyko46 · #3 04-01-2010, 06:31 PM

According with instructions from Haynes Book for Mercedes Benz, it should be bleed before connecting to brake lines otherwise air from empty master cylinder will go to te brake lines. "There is supposed to have brake fluid only, no air, coming from master cylinder before connect any brake line" the book says.

JohnM. · #4 04-01-2010, 06:48 PM

Haynes manuals (for any car) appear to be written by a lobotomized monkey. I have never bench bled any MC before installing. Try doing it as I said, if air goes into the brake lines that's fine. Which is why you bleed each wheel until there are no more air bubbles, just clear fluid coming thru.

compress ignite · #5 04-01-2010, 06:55 PM

X 2
(On the Lobotomized Primate Authors)